The present invention relates to a telephone system using a wireless LAN. Specifically, it relates to number roaming control.
In a computer network, computers are mutually connected via a network. The Internet is known as a computer network via which computers of different types are mutually connected. The Internet uses a TCP/IP (transmission control protocol/internet protocol) as a network protocol. The TCP/IP is a hierarchical protocol formed of five layers. The IP is used as a typical protocol for a network layer, and the TCP is used as a typical protocol for a transport layer. For this reason, the name “TCP/IP” is widely used.
The IP includes a function of allocating addresses to individual computers connected to the Internet and a function of connecting a channel thereto. For the addresses, the IP uses IP addresses each represented by a 32-bit integer. Each of the IP addresses is allocated to a network interface of each of the computers; that is, the IP address is not allocated to the computer. As such, for a computer such as a router including a plurality of network interfaces, a unique IP address is allocated to each of the interfaces.
A LAN (local area network) is a locally facilitated network system for connecting a variety of computers, such as servers, workstations, and personal computers, distributed in a relatively narrow area, such as a same building or a same site. Widely used operating configurations include a configuration in which many hosts share one transmission medium. As a transmission control technique, MAC (media access control) is known. The MAC refers to access control that allows a plurality of nodes to smoothly use a local-area cable. The MAC is positioned over a datalink lower sublayer of an OSI (open systems interconnection) model, and implements a datalink layer function by operating in cooperation with an LLC (logic link control).
MAC addresses are standardized datalink layer addresses necessary for all ports or devices connected to the LAN. Another device in the network uses these addresses, thereby locates a specific port in the network, and generates and updates routing table and a data structure. The MAC address has a 6-byte length, and is controlled according to IEEE. The MAC address is also known as a hardware address, a MAC layer address, or a physical address.
An ARP (address resolution protocol) converts an IP address into a MAC address of, for example, Ethernet (registered trademark). When data is accessed for transmission from the IP layer, a destination IP address needs to be converted into a MAC address.
In a telephone service using the IP, particularly in an IP telephone service using a wireless LAN, audio quality varies depending on the traffic condition in the network. The “wireless LAN” refers to a LAN using transmission channels, such as an electromagnetic waves (radio waves) and light (infrared ray). A LAN using cable transmission channels is called a “wired LAN”.
The “IP telephone” refers to a telephone using the IP. Specifically, the IP telephone includes a means for performing communication via an IP telephone network (IP network). Unlike an ordinary telephone, the IP telephone digitizes (packetize) sounds for transmission. The “IP telephone network” refers to an IP-used telephone network that enables IP-based communication, although the network is not specifically limited to the telephone network. An IP address (equivalent to a telephone number of an ordinary telephone) of a communication destination is entered to perform transmission to a communication destination by using the IP telephone. When a main device of an IP telephone is usable, the IP address can be correlated to either an extension number or a nickname (such as an arbitrary character string), so that transmission can be performed using the extension number or the nickname. The “IP communication” refers to communication being carried out through an IP telephone.
A telephone system using a wireless LAN is known. The telephone system includes a main device, a plurality of wireless-LAN base stations connected to the main device via a wired LAN, and a plurality of wireless telephones that communicate with the wireless LAN base stations via the wireless LAN. The main device is connected to a network such as a public network or the Internet. In this case, an SSID (service set ID) is set as a wireless-LAN base station zone identifier. The SSID is represented by an arbitrary character string of 32 or fewer characters.
In the conventional telephone system configured as described above, the main device performs transmits data to a destination regardless of the network condition. As such, the system can enter a busy state depending on the traffic condition, thereby disabling incoming data to be received.
Known prior-art publications related to the present invention includes Japanese Unexamined Patent Publication No. 2001-8266 (which hereinbelow will be referred to as a “prior-art publication 1”). The prior-art publication 1 discloses the provision of an “automatic answering telephone system” for implementing a compromise at a low cost between the provision of a cheap automatic-answering-telephone function service to users and the improvement in efficiency of the amount of transmission. According to the automatic-answering-telephone system disclosed in the prior-art publication 1, internet-automatic-answering-telephone transfer function devices and a portable-telephone position storage device are connected to exchangers that operate for portable telephones. The internet automatic-answering-telephone transfer function devices are connected to the Internet. The portable-telephone position storage device stores information of a registration position of each of the portable telephones, automatic-answering-function setting information therefor, and information of connection to the Internet automatic-answering-telephone transfer function devices. When automatic-answer information has been received from one of the portable telephones, the information is stored into the internet-automatic-answering-telephone transfer function device connected to the exchanger under which the portable telephone is controlled. In the case of performing a playback of an automatic-answering-telephone message, a request packet requesting retrieval of the automatic-answer information is transmitted from one of the internet-automatic-answering-telephone transfer function devices positioned close to the portable phone that has issued a playback request to all the internet-automatic-answering-telephone transfer function devices in a broadcast mode via the Internet, and is thereby collected.